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Overseeding: Tackling Grassland Underperformance

July 14, 2021

All grassland farmers can identify underperforming fields on their farms. Stock carrying capacity and performance may be reduced, while silage quantity and quality may also see a marked decline. With on-farm pressures on grazing and/or silage production, full reseeds may be difficult to undertake. Kevin McGrath, Beef and Sheep Adviser with CAFRE states, “Our unpredictable weather, difficulty getting contractors when required, and our own available time will often contribute to a cycle of continuous grassland underperformance.”

Overseeding should be considered as a practical working solution on farm. Coming in at just over half the cost of a full reseed, it has been shown to increase production by up to 40% in the short to medium term. This increased production can help reduce costs on farm while also increasing output through animal performance.

Controlling competition from the existing sward can determine the success or failure of any overseeding programme. The existing sward must be controlled to allow the introduced seedlings to develop and compete.

In order to control competition, grazing swards should be grazed tightly before and up to 10 days after seeding. Dry ewes are excellent for the job.

Silage swards should be seeded immediately after cutting. The heavier the crop of grass removed the longer it will take for the existing sward to recover.  As an alternative, a suitable herbicide can be applied to control the existing sward.

The most successful months to reseed are March, April and July through to September. Grass growth in May and June is at its peak and should be avoided.

Soil fertility must be corrected with adequate lime P and K applied. Nitrogen should only be applied 4 weeks after sowing. This will avoid the old sward out-competing the newly established plants.

Kevin advises that tetraploid ryegrass varieties are best suited for overseeding. They have a larger seed with more energy and an aggressive growth pattern which will ensure better establishment. Seed should be sown at 10 kg/ac. Overseeding should not take place during periods of dry weather to ensure seed/plant survival.

If you have a situation where a grass sward is open with clear ground visible, a grass harrow can be used to create an appropriate soil tilth. This will involve a number of passes to ensure adequate seed to soil contact. The chain harrow will also help remove poorer performing weed grasses as they are shallower rooting and easier to remove than the ryegrass varieties. Following harrowing, apply the seed, P and K fertiliser and light roll.

In situations where the ground is less open, with greater competition, a slot seeding system may be best. Some ‘Stitching in’ machines place seed 2-5cm apart while others place both seed and fertiliser in a 4cm rotavated slot. It is recommended to undertake an additional diagonal run across the field to ensure a denser sward.

The newly sown grass should be left for 5 – 6 weeks and assessed for its suitability to lightly graze. Monitor weed numbers, applying an appropriate herbicide as necessary. 

Kevin summarises by highlighting that overseeding has been shown to be a useful tool in improving the productivity of damaged and underperforming swards on farm. Success is dependent on reducing competition, providing appropriate fertility and allowing the new grass seed time to establish and develop.